Elevationally-extending string of memory cells and methods of forming an elevationally-extending string of memory cells

ABSTRACT

A method that is part of a method of forming an elevationally-extending string of memory cells comprises forming an intervening structure that is elevationally between upper and lower stacks that respectively comprise alternating tiers comprising different composition materials. The intervening structure is formed to comprise an elevationally-extending-dopant-diffusion barrier and laterally-central material that is laterally inward of the dopant-diffusion barrier and has dopant therein. Some of the dopant is thermally diffused from the laterally-central material into upper-stack-channel material. The dopant-diffusion barrier during the thermally diffusing is used to cause more thermal diffusion of said dopant into the upper-stack-channel material than diffusion of said dopant, if any, into lower-stack-channel material. Other embodiments, including structure independent of method, are disclosed.

TECHNICAL FIELD

Embodiments disclosed herein pertain to elevationally-extending stringsof memory cells and to methods of forming such.

BACKGROUND

Memory provides data storage for electronic systems. Flash memory is onetype of memory, and has numerous uses in computers and other devices.For instance, personal computers may have BIOS stored on a flash memorychip. As another example, flash memory is used in solid state drives toreplace spinning hard drives. As yet another example, flash memory isused in wireless electronic devices as it enables manufacturers tosupport new communication protocols as they become standardized, and toprovide the ability to remotely upgrade the devices for improved orenhanced features.

A typical flash memory comprises a memory array that includes a largenumber of memory cells arranged in row and column fashion. The flashmemory may be erased and reprogrammed in blocks. NAND may be a basicarchitecture of flash memory. A NAND cell unit comprises at least oneselecting device coupled in series to a serial combination of memorycells (with the serial combination commonly being referred to as a NANDstring). Example NAND architecture is described in U.S. Pat. No.7,898,850.

Memory cell strings may be arranged to extend horizontally orvertically. Vertical memory cell strings reduce horizontal area of asubstrate occupied by the memory cells in comparison tohorizontally-extending memory cell strings, albeit typically at theexpense of increased vertical thickness. Vertical memory cell stringsare usually fabricated in multiple stacks or decks which facilitates themanufacturing thereof. Each stack includes vertically-alternating tierscomprising control gate material of individual charge-storagetransistors that vertically alternate with insulating material. Achannel pillar extends through each of the stacks and a conductiveinterconnect electrically couples the channels of immediatelyelevationally adjacent channel pillars together. Conductively-dopedpolysilicon is one example material for the conductive interconnect.Such may, for example, be conductively doped with phosphorus (an n-typematerial). The phosphorus can diffuse above and below the polysiliconinto the upper and lower stack channel materials. More may diffuse downthan up which can adversely impact programmable memory cells in theelevationally outermost portion of the lower stack.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic sectional view of a portion of anelevationally-extending string of memory cells in accordance with anembodiment of the invention.

FIG. 1A is an enlarged portion of FIG. 1, and an outline of which isshown in FIG. 1.

FIG. 2 is a sectional view taken through line 2-2 in FIG. 1.

FIG. 3 is a sectional view taken through line 3-3 in FIG. 1.

FIG. 4 is a sectional view taken through line 4-4 in FIG. 1.

FIG. 5 is a diagrammatic sectional view of a portion of anelevationally-extending string of memory cells in accordance with anembodiment of the invention.

FIG. 5A is an enlarged portion of FIG. 5, and an outline of which isshown in FIG. 5.

FIG. 6 is a diagrammatic sectional view of a portion of anelevationally-extending string of memory cells in accordance with anembodiment of the invention.

FIG. 6A is an enlarged portion of FIG. 6, and an outline of which isshown in FIG. 6.

FIG. 7 is a diagrammatic sectional view of a portion of anelevationally-extending string of memory cells in accordance with anembodiment of the invention.

FIG. 7A is an enlarged portion of FIG. 7, and an outline of which isshown in FIG. 7.

FIG. 8 is a diagrammatic sectional view of a portion of anelevationally-extending string of memory cells in accordance with anembodiment of the invention.

FIG. 8A is an enlarged portion of FIG. 8, and an outline of which isshown in FIG. 8.

FIG. 9 is a diagrammatic sectional view of a portion of anelevationally-extending string of memory cells in accordance with anembodiment of the invention.

FIG. 9A is an enlarged portion of FIG. 9, and an outline of which isshown in FIG. 9.

FIG. 10 is a diagrammatic sectional view of a portion of anelevationally-extending string of memory cells in accordance with anembodiment of the invention.

FIG. 10A is an enlarged portion of FIG. 10, and an outline of which isshown in FIG. 10.

FIG. 11 is a diagrammatic sectional view of a portion of anelevationally-extending string of memory cells in accordance with anembodiment of the invention.

FIG. 11A is an enlarged portion of FIG. 11, and an outline of which isshown in FIG. 11.

FIG. 12 is a diagrammatic sectional view of a substrate fragment inprocess in accordance with an embodiment of the invention.

FIG. 13 is a view of the FIG. 12 substrate fragment at a processing stepsubsequent to that shown by FIG. 12.

FIG. 14 is a view of the FIG. 13 substrate fragment at a processing stepsubsequent to that shown by FIG. 13.

FIG. 15 is a view of the FIG. 14 substrate fragment at a processing stepsubsequent to that shown by FIG. 14.

FIG. 16 is a view of the FIG. 15 substrate fragment at a processing stepsubsequent to that shown by FIG. 15.

FIG. 17 is a view of the FIG. 16 substrate fragment at a processing stepsubsequent to that shown by FIG. 16.

FIG. 18 is a view of the FIG. 17 substrate fragment at a processing stepsubsequent to that shown by FIG. 17.

FIG. 19 is a view of the FIG. 18 substrate fragment at a processing stepsubsequent to that shown by FIG. 18.

FIG. 20 is a diagrammatic sectional view of a substrate fragment inprocess in accordance with an embodiment of the invention.

FIG. 21 is a view of the FIG. 20 substrate fragment at a processing stepsubsequent to that shown by FIG. 20.

FIG. 22 is a view of the FIG. 21 substrate fragment at a processing stepsubsequent to that shown by FIG. 21.

FIG. 23 is a view of the FIG. 22 substrate fragment at a processing stepsubsequent to that shown by FIG. 22.

FIG. 24 is a view of the FIG. 23 substrate fragment at a processing stepsubsequent to that shown by FIG. 23.

FIG. 25 is a view of the FIG. 24 substrate fragment at a processing stepsubsequent to that shown by FIG. 24.

FIG. 26 is a view of the FIG. 25 substrate fragment at a processing stepsubsequent to that shown by FIG. 25.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Embodiments of the invention encompass an elevationally-extending stringof memory cells and methods of forming an elevationally-extending stringof memory cells.

A first embodiment elevationally-extending string of memory cells isshown and described with reference to FIGS. 1-4. Such includes aconstruction 10 comprising a base substrate 12 that may include any oneor more of conductive/conductor/conducting (i.e., electrically herein),semiconductive, or insulative/insulator/insulating (i.e., electricallyherein) materials. In this document, a conductor/conductive/conductingmaterial or region (including a conductively-dopedsemiconductor/semiconductive/semiconducting material or region) isconductive by having compositional intrinsic conductivity of at least 1Siemen/cm (i.e., at 20° C. everywhere herein) as opposed to conductivitythat could occur by movement of positive or negative charges through athin material that is otherwise intrinsically insulative orsemiconductive. Further, and by way of example only, a maximumconductance may be 1×10⁴ Siemens/cm. Aninsulator/insulative/insulating/dielectric material or region isinsulative by having compositional intrinsic conductivity of no greaterthan 1×10⁻¹⁰ Siemen/cm (i.e., it is electrically resistive as opposed tobeing conductive or semiconductive). Further, and by way of exampleonly, a minimum conductance may be 1×10⁻¹² Siemen/cm. Asemiconductor/semiconductive/semiconducting material or region that isnot doped to be conductive is semiconductive by having compositionalintrinsic conductivity of less than 1 Siemen/cm and greater than 1×10⁻¹⁰Siemen/cm.

Various materials are shown above base substrate 12. Materials may beaside, elevationally inward, or elevationally outward of the FIGS.1-4-depicted materials. For example, other partially or whollyfabricated components of integrated circuitry may be provided somewhereabove, about, or within substrate 12. Control and/or other peripheralcircuitry for operating components within the memory array may also befabricated, and may or may not be wholly or partially within a memoryarray or sub-array. Further, multiple sub-arrays may also be fabricatedand operated independently, in tandem, or otherwise relative oneanother. As used in this document, a “sub-array” may also be consideredas an array.

Construction 10 is shown as comprising two elevationally-extendingstrings 14 of memory cells 16 individually comprising a programmablecharge-storage-field effect transistor 18. Construction 10 comprises anupper stack or deck 20 that is elevationally over a lower stack or deck22. Upper and lower stacks 20, 22 individually comprisevertically-alternating tiers 24, 26 comprising control-gate material 28(in tiers 24) of individual charge-storage transistors 18 alternatingwith insulating material 30 (in tiers 26). Example conductivecompositions for control gate material 28 are one or more of elementalmetal, a mixture or alloy of two or more elementals, conductive metalcompounds, and conductively-doped semiconductive materials. Exampleinsulating compositions for material 30 are one or more of silicondioxide and silicon nitride. Example thicknesses for materials 28 and 30are 350 Angstroms and 200 Angstroms, respectively.

Only a few alternating tiers 24, 26 are shown with respect to each stack20, 22, although each stack would likely have dozens or more of each oftiers 24 and 26. Additionally, only two stacks 20 and 22 are shown,although one or more additional stacks (not shown) may also be provided.Further and regardless, each stack need not be fabricated identicallyrelative another stack nor include identical materials. Regardless, anyconstruction in accordance with the invention will have some upper stack20 and an adjacent lower stack 22. Transistors 18 in one or more tiersin the lowest part of upper stack 20 and uppermost part of lower stack22 may be “dummy” which may or may not store data. Further, an array ofmemory cells will likely include many more than twoelevationally-extending strings 14. The description largely proceedswith respect to construction and method associated with a single string14, although others if not all strings within an array will likely havethe same attributes. In some embodiments, elevationally-extending string14 is vertical or within 10° of vertical.

An upper-stack-channel pillar 32 extends through multiple ofvertically-alternating tiers 24, 26 in upper stack 20. Alower-stack-channel pillar 34 extends through multiple ofvertically-alternating tiers 24, 26 in lower stack 22. Channel pillars32 and 34 are shown as comprising channel material 33 and as beinghollow channel pillars that are internally filled with insulatormaterial 36 (e.g., silicon dioxide and/or silicon nitride). Alternately,one or both of the upper and lower-stack-channel pillars may benon-hollow, for example comprising channel material extending completelydiametrically-across the pillar (e.g., no internal insulator material 36and not shown). Regardless, the channel pillar material 33 ideallycomprises doped semiconductive material (e.g., polysilicon) havingchannel-conductivity-modifying dopant(s) present in a quantity thatproduces intrinsic semiconductor properties enabling the upper and lowerchannel pillars to operably function as switchable “on” and “off”channels for the individual memory cells for control-gate voltage aboveand below, respectively, a suitable threshold voltage (Vt) depending onprogramming state of the charge-storage transistor for the respectiveindividual memory cell. An example such dopant quantity is from 5×10¹⁷atoms/cm³ to 5×10¹⁸ atoms/cm³. Channel material 33 may be p-type orn-type. Channel material 33 may be semiconductive having conductivity ofless than 1 Siemen/cm and greater than 1×10⁻¹⁰ Siemen/cm (i.e.,intrinsic to the material at 0 Volt gate field).

Insulative-charge-passage material 38 (e.g., one or more of silicondioxide and silicon nitride), charge-storage material 40 (e.g., materialsuitable for use in floating gates or charge-trapping structures, suchas, for example, one or more of silicon, silicon nitride, nanodots,etc.), and a charge-blocking region 42 are laterally betweenupper/lower-stack-channel pillars 32, 34, respectively, and control-gatematerial 28 in tiers 24. A charge block may have the following functionsin a memory cell: In a program mode, the charge block may prevent chargecarriers from passing out of the charge-storage material (e.g.,floating-gate material, charge-trapping material, etc.) toward thecontrol gate, and in an erase mode the charge block may prevent chargecarriers from flowing into the charge-storage material from the controlgate. Accordingly, a charge block may function to block charge migrationbetween the control-gate region and the charge-storage material ofindividual memory cells. Such a charge-blocking region is laterally(e.g., radially) outward of charge-passage material 38 and laterally(e.g., radially) inward of conductive-control-gate material 28. Anexample charge-blocking region as shown comprises insulator material 42(e.g., one or more of silicon nitride, silicon dioxide, hafnium oxide,zirconium oxide, etc.). By way of further examples, a charge-blockingregion may comprise a laterally (e.g., radially) outer portion of thecharge-storage material (e.g., material 40) where such charge-storagematerial is insulative (e.g., in the absence of anydifferent-composition material between insulative-charge-storagematerial 40 and control-gate material 28). Regardless, as an additionalexample, an interface of a charge-storage material and conductivematerial of a control gate may be sufficient to function as acharge-blocking region in the absence of anyseparate-composition-insulator material (e.g., in the absence ofmaterial 42). Further, an interface 57 of control-gate material 28 withmaterial 42 (when present) in combination with insulator material 42 maytogether function as a charge-blocking region, and as alternately oradditionally may a laterally-outer region of aninsulative-charge-storage material (e.g., a silicon nitride material40).

Base substrate 12 may comprise conductively-doped semiconductivematerial comprising source lines (not shown) connecting with alowest-stack-channel pillar and which may comprise a portion ofcircuitry for the vertical string of memory cells. Additionally, aconductive line (not shown) may connect with an uppermost-stack-channelpillar and which may comprise a portion of circuitry for theelevationally-extending string of memory cells.

Individual memory cells 16 may comprise other alternate oryet-to-be-developed constructions that include anelevationally-extending-upper-stack-channel pillar and anelevationally-extending-lower-stack-channel pillar, and may befabricated by any method. For example, and by way of example only,construction 10 has memory cell materials 38, 40, and 42 elevationallybetween underlying and overlying insulator material 30. Such may bemanufactured by a so-called “gate first” process whereby an opening inwhich the channel pillar is formed is first-formed through alternatingtiers of conductive material 28 and insulator material 30. Conductivematerial 28 is then laterally recessed back from sidewalls of thatopening by isotropic etching, followed by deposition of materials 42,40, and 38 into the annular recesses so formed. Such materials are thenetched to remove them from being outside of the annular recesses,followed by deposition of the channel material. Alternately, onlymaterials 42 and 40 may be deposited into the recesses, followed bydeposition of insulative-charge-passage material 38 and then depositionof the channel material (e.g., after etching materials 42 and 40 frombeing within the opening outside of the annular recesses).

Alternately and by way of example only, the memory cells may befabricated such that materials 38, 40, and 42 are not elevationallybetween (not shown) insulator material 30 that is in different tiers 26,for example by a so-called “gate last” or “replacement gate” process.There, a stack may be manufactured to comprise tiers ofvertically-alternating different composition insulating materials, andan opening for the channel material is then formed there-through. Then,materials 42, 40, and 38 are deposited as circumferential linings insuch opening, followed by deposition of the channel material into theopening. Then, slits are etched through the stack to produce a desiredcontrol gate pattern, and one of the insulator materials isisotropically etched away to leave void space elevationally between theother insulating material (e.g., 30) that is in different tiers. Theconductive control gate material is there-after conformally deposited tofill the slits and void spaces, followed by anisotropic etching of theconductive material from the slits, thus leaving patterned controlgates. Also and regardless, construction 10 is shown as comprising asingle memory cell 16 about the channel pillar in each tier 24 in astring 14. Alternately, and by way of example only, any existing oryet-to-be-developed construction may be used wherein two or more memorycells are circumferentially spaced about the channel in a single tier ina given string (not shown).

A plurality of materials is shown elevationally between upper stack 20and lower stack 22. Such might be fabricated separately from thefabrication of upper stack 20 and lower stack 22, or may be fabricatedin whole or in part when fabricating upper stack 20 and/or lower stack22. Accordingly, unless otherwise stated, one or more of suchintervening materials might be considered as part of one or both ofupper stack 20 and lower stack 22. Such intervening materials are shownas including different insulating materials 50 (e.g., 100 Angstroms ofSiO₂), 52 (e.g., 540 Angstroms of Al₂O₃), 54 (e.g., 600 Angstroms ofSi₃N₄), and 56 (e.g., 200 Angstroms of SiO₂). Upper-stack-channel pillar32 is shown as having a lower portion thereof that bulges radiallyoutward within or into dielectric material 52, which may occur as anartifact of manufacture wherein insulator material 52 is wetisotropically etched to expose material there-below before formingchannel pillar 32.

An intervening structure 60 is elevationally between upper stack 20 andlower stack 22. In some embodiments, intervening structure 60 is aconductive interconnect which electrically couples upper-stack-channelpillar 32 and lower stack-channel pillar 34 together. In the context ofthis document, a conductive interconnect has at least some conductivematerial between the upper and lower stacks which electrically couplesthe upper and lower channel pillars together. In one embodiment and asshown, a conductive interconnect 60 comprises anelevationally-extending-dopant-diffusion barrier 62 (FIG. 1A) and alaterally-central material 64 (i.e., at least some of which is laterallycentral relative to conductive interconnect 60), with barrier 62 beinglaterally outward of central material 64. In one embodiment and asshown, barrier 62 comprises an elevationally-extending cylinder.

In one embodiment, laterally-central material 64 has an uppermost region69 that is conductive. In one embodiment, laterally-central material 64has a lowermost region (e.g., a base 70) which may be conductive,semiconductive, or insulative and, regardless, in one embodimentcomprises a laterally-extending-dopant-diffusion barrier. Exampleuppermost region 69 is shown extending elevationally inward toregion/base 70, although uppermost region 69 may be elevationally lessthick, for example only in an uppermost fraction of conductiveinterconnect 60 that is less than half of the elevation of conductiveinterconnect 60, and may for example only be that portion of material 64that is higher than surface 66 of diffusion barrier 62. Regardless, inone embodiment, uppermost region 69 comprises conductively-dopedsemiconductive material (e.g., polysilicon). Alternately by way ofexample only, material 69 might comprise metal material (e.g., TiN, WN,Ti, W, Cu, etc.) and which may include dopant therein. In one embodimentand as shown, upper-stack-channel pillar 32 is directly againstconductive-uppermost region 69 of central material 64. Additionally oralternately considered, a lowest portion of upper channel material 33may be conductively-doped semiconductive material, for example which hasbeen conductively doped with conductivity-enhancing dopant from thermaldiffusion of conductivity-enhancing dopant present in uppermost region69 into the lowest portion of upper channel material 33 (i.e., whenconductivity-enhancing dopant to material 33 is in uppermost region 69).Thereby, and regardless of how such occurred, and in one embodiment,uppermost region 69 and conductive interconnect 60 may extend upwardly(not shown) into what is shown as the lowest portion of upper channelmaterial 33 of upper-stack-channel pillar 32.

In one embodiment, base 70 has dopant-diffusion-barrier properties(i.e., it blocks diffusion of dopant there-through) and is directlyagainst and extends laterally between cylindrical sidewalls ofdopant-diffusion barrier 62. Accordingly, base 70 of laterally-centralmaterial 64 may have dopant-diffusion-barrier properties in someembodiments. In one embodiment, diffusion barrier 62 is insulative(e.g., silicon dioxide, silicon nitride, aluminum oxide, hafnium oxide,etc.) and in one embodiment base 70 is insulative. In one embodiment,diffusion barrier 62 has an elevationally-outermost surface 66 that islower than an elevationally-outermost surface 67 of conductiveinterconnect 60.

Topping material 72 is above elevationally-outermost surface 66, and inone embodiment directly there-against, of diffusion barrier 62. In someembodiments, topping material 72 is conductive and would be so in theembodiment of FIGS. 1-4. In one embodiment, topping material 72 isdopant transmissive, for example as may occur by thermal diffusion of aconductivity-modifying dopant from a dopant-containing uppermostregion/material 69 as described in more detail below. Topping material72 may be of the same or different composition as that of upper region69 of central material 64, with example same composition being shown bya dashed interface line 73 between upper region 69 and topping material72. In one embodiment and as shown, topping material 72 comprises acylinder. In one embodiment and as shown, upper-stack-channel pillar 32is not directly against topping material 72, and yet may be so in otherembodiments.

Side material 74 extends elevationally laterally outward of diffusionbarrier 62, and is at least one of conductive and semiconductive. In oneembodiment, side material 74 from top to bottom is conductive, in oneembodiment from top to bottom is semiconductive, and in one embodimentis both conductive and semiconductive (e.g., it has different stackedregions that are individually one of conductive and semiconductive).Example conductive-side materials includeconductively-doped-semiconductive material and metal material. Examplesemiconductive material includes undoped silicon or doped silicon havinga dopant concentration below a threshold whereby the material becomesconductive as defined above.

In one embodiment, side material 74 has an elevationally-outermostregion that is conductive, and in one such embodiment has anelevationally-innermost region that is semiconductive. Wheresemiconductive, such elevationally-innermost region may be anupwardly-extending portion of lower-stack-channel pillar 34. Forexample, and by way of example only, FIG. 1 shows an exampleelevationally-outermost region 75 that may be conductive and anelevationally-innermost region 76 that may be semiconductive andcomprise an upwardly-extending portion 79 of lower-stack channel pillar34. An example interface line 77 is shown between outermost region 75and innermost region 76 to diagrammatically show an example demarcationbetween regions 75 and 76. However more likely, interface 77 would be aregion extending into regions 75 and 76 whereinconductivity-modifying-dopant concentration varies from high to lowmoving elevationally inward, and in one embodiment.

An alternate example construction 10 a is shown in FIGS. 5 and 5A. Likenumerals from the above-described embodiments have been used whereappropriate, with some construction differences being indicated with thesuffix “a”. Intervening structure 60 a is shown as having centralmaterial 64 a that is devoid of bottom/base region 70 that is in FIG. 1.Any other attribute(s) or aspect(s) as shown and/or described hereinwith respect to other embodiments may be used.

Another example alternate construction 10 b is shown in FIGS. 6 and 6A.Like numerals from the above-described embodiments have been used whereappropriate, with some construction differences being indicated with thesuffix “b”. Intervening structure 60 b is shown as comprising adiffusion barrier 62 b which does not extend elevationally outward tothe degree which barriers 62 and 62 a do in FIGS. 1-4 and FIGS. 5, 5A,respectively. Elevational thicknesses of regions or materials 72 b, 75b, 76 b, and 79 b may change, for example as shown. Any otherattribute(s) or aspect(s) as shown and/or described herein with respectto other embodiments may be used.

Another example alternate embodiment construction 10 c is shown in FIGS.7 and 7A. Like numerals from the above-described embodiments have beenused where appropriate, with some construction differences beingindicated with the suffix “c”. Upper-stack-channel pillar 32 c isdirectly against conductive-topping material 72, and in one suchembodiment as shown is not directly against central material 64 (e.g.,no material 33 extending between sidewalls of material 33 in thedepicted cross-section). In one such embodiment, uppermost region 69 ofcentral material 64 may not be conductive as, for example, upper channelpillar 32 c conductively connects with lower channel pillar 34 through aconductive-topping material 72, and regardless of whether an upperregion 75 of side material 74 is semiconductive or conductive.Analogously as described above, a lowest portion of upper channelmaterial 33 may be conductively-doped-semiconductive material, forexample which has been conductively doped with conductivity-enhancingdopant from thermal diffusion of conductivity-enhancing dopant presentin uppermost region 69 and/or into the lowest portion of upper channelmaterial 33. Thereby, and regardless of how such occurred, and in oneembodiment, conductive-topping material 72 may extend upwardly (notshown) into what is shown as the lowest portion of upper channelmaterial 33 of upper-stack-channel pillar 32. Any other attribute(s) oraspect(s) as shown and/or described herein with respect to otherembodiments may be used.

Another example embodiment construction 10 d is shown in FIGS. 8 and 8A.Like numerals from the above-described embodiments have been used whereappropriate, with some construction differences being indicated with thesuffix “d”. A conductive-topping material 72 d extends laterally ofelevationally-outermost surface 66 of diffusion barrier 62 above sidematerial 74 d and central material 64 d (e.g., material 72 d isconductive from side-to-side in horizontal cross-section). In oneembodiment, topping material 72 d comprises metal material and in oneembodiment comprises conductively-doped semiconductive material. In oneembodiment, side material 74 d has an elevationally-innermost region 76that is semiconductive, and in one such embodiment may comprise aconductive upper region 75 d. Any other attribute(s) or aspect(s) asshown and/or described herein with respect to other embodiments may beused.

Another alternate embodiment construction 10 e is shown in FIGS. 9 and9A. Like numerals from the above-described embodiments have been usedwhere appropriate, with some construction differences being indicatedwith the suffix “e”. FIGS. 9 and 9A show an example wherein upperstack-channel pillar 32 e is directly above central material 64 (andconductive-topping material 72) yet is not directly above side material74. Analogously as described above, a lowest portion of upper channelmaterial 33 may be conductively-doped-semiconductive material, forexample which has been conductively doped with conductivity-enhancingdopant from thermal diffusion of conductivity-enhancing dopant presentin uppermost region 69 and/or conductive-topping material 72 into thelowest portion of upper channel material 33. Thereby, and regardless ofhow such occurred, and in one embodiment, conductive-topping material 72may extend upwardly (not shown) into what is shown as the lowest portionof upper channel material 33 of upper-stack-channel pillar 32. Any otherattribute(s) or aspect(s) as shown and/or described herein with respectto other embodiments may be used.

Another example embodiment construction 10 f is shown in FIGS. 10 and10A. Like numerals from the above-described embodiments have been usedwhere appropriate, with some construction differences being indicatedwith the suffix “f”. Laterally-central material 64 hasconductivity-modifying dopant therein. Conductively-doped-semiconductivematerial 75 is elevationally between upper-stack-channel pillar 32 f andlower-stack-channel pillar 34 aside topping material 72. Toppingmaterial 72 may not be conductive in this embodiment, but ideally willbe dopant transmissive. In one embodiment, the topping material isconductive. In one embodiment, the conductively-doped-semiconductivematerial is directly against the topping material. In one embodiment,the conductively-doped-semiconductive material and the topping materialare of the same composition. Analogously as described above, a lowestportion of upper channel material 33 may beconductively-doped-semiconductive material, for example which has beenconductively doped with conductivity-enhancing dopant from thermaldiffusion of conductivity-enhancing dopant present in uppermost region69 and/or topping material 72 into the lowest portion of upper channelmaterial 33. Thereby, and regardless of how such occurred, and in oneembodiment, conductive region 75 may extend upwardly (not shown) intowhat is shown as the lowest portion of upper channel material 33 ofupper-stack-channel pillar 32. Any other attribute(s) or aspect(s) asshown and/or described herein with respect to other embodiments may beused.

Another alternate example embodiment construction 10 g is shown in FIGS.11 and 11A. Like numerals from the above-described embodiments have beenused where appropriate, with some construction differences beingindicated with the suffix “g”. Conductive interconnect 60 g comprisesconductive-side material 74 laterally outward of and extendingelevationally along laterally-central material 64. Lower-stack-channelpillar 34 is directly against conductive-side material 74. By way ofexamples, side material 74 may comprise metal material and/or maycomprise conductively-doped semiconductive material. In one embodiment,lower-stack-channel pillar 34 is directly against anelevationally-innermost surface 81 of side material 74. In oneembodiment and as shown, side material 74 comprises anelevationally-extending cylinder. FIG. 11A shows an example embodimentwherein diffusion barrier 62 is not shown, whereas adopant-diffusion-barrier base/bottom 70 is shown. Any other attribute(s)or aspect(s) as shown and/or described herein with respect to otherembodiments may be used.

Embodiments of the invention encompass methods of forming anelevationally-extending string of memory cells including, for exampleand by way of example only, one or more of the above-identifiedconstructions. Example such embodiments are described with reference toFIGS. 12-26. Like numerals from the above-described embodiments havebeen used where appropriate, including for predecessor constructions andmaterials. Any of the method embodiments may have any of the attributesdescribed above with respect to structure embodiments and vice versa.

Referring to FIG. 12, lower stack 22 has been formed to comprisefirst-alternating tiers 24, 26 of first-lower-stack material 44 andsecond-lower-stack material 30 comprising different compositions.Insulator material 56, 54 has been formed above lower stack 22 and alower opening 80 has been formed to extend through insulator material56, 54 and multiple of first-alternating tiers 24, 26.

Referring to FIG. 13, and by way of example only, material 44 (notshown) has been removed and replaced with materials 28, 42, 40, and 38as, for example, shown in the FIG. 1 embodiment, and in what may beconsidered as so called “gate first” processing for example as describedabove. Alternately, so called “gate last” processing may be used forexample as described above. Regardless, lower-stack-channel material 33has been formed in lower opening 80. Such channel may be formed as ahollow channel or as a solid pillar, however, with material 33comprising an elevationally-outermost portion that is both againstsidewalls of lower opening 80 and less-than-fills anelevationally-outermost portion of lower opening 80. Alternatelyconsidered or stated, a lower portion of upper channel material 33 maybe a solid pillar extending completely diametrically across loweropening 80 wherein at least an elevationally-outermost portion thereofless-than-fills the elevationally-outermost portion of lower opening 80,for example being cylindrical as shown in FIGS. 1-4. FIG. 13 showsinsulator material 36 (e.g., silicon dioxide formed in a spin-ondielectric manner) centrally within lower opening 80.

Referring to FIG. 14, insulator material 36 has been elevationallyrecessed (e.g. by isotropic etching) selectively relative to exposedlower-stack-channel material 33.

Referring to FIG. 15, elevationally-extending-dopant-diffusion barriermaterial 62 has been formed around lower opening 80 laterally inward ofthe elevationally-outermost portion of lower-stack-channel material 33.Remaining volume of lower opening 80 has then been filled withlaterally-central material 64 laterally inward of diffusion barriermaterial 62. FIG. 16 shows material 62 and 64 as having been planarizedback at least to an elevationally-outmost surface 83 of insulatormaterial 56, 54.

Referring to FIG. 17, dopant-diffusion barrier 62 has been elevationallyrecessed relative to elevationally-outermost surface 83 of insulatormaterial 56, 54 that is adjacent lower opening 80 to formdopant-diffusion-barrier 62 to have an elevationally-outermost surface66 that is lower than elevationally-outermost surface 83 of insulatormaterial 54, 56 that is adjacent lower opening 80. Such may beaccomplished, by way of example, by any suitable wet or dry etchingwhich etches material 62 selectively relative to the other exampleexposed materials. In one embodiment, the elevationally recessing ofdopant-diffusion barrier 62 also elevationally recesses such barrierrelative to an elevationally-outermost surface 84 of laterally-centralmaterial 64/region 69 whereby barrier surface 66 is lower thancentral-material surface 84. In one embodiment, the elevationallyrecessing of dopant-diffusion barrier 62 also elevationally recessessuch barrier relative to an elevationally outermost surface oflower-stack-channel material 33 whereby barrier surface 66 is lower thansuch lower-stack-channel material surface.

Referring to FIG. 18, topping material 72 has been formed aboveelevationally-outermost surface 66 of recessed dopant-diffusion barrier62. In one embodiment and as shown, topping material 72 is formeddirectly against the recessed dopant-diffusion barrier, and in one suchembodiment directly against the elevationally-outermost surface 66 ofrecessed dopant-diffusion barrier 62.

Referring to FIG. 19, the construction of FIG. 18 has been planarizedback at least to elevationally-outermost surface 83 of insulatormaterial 54, 56.

Subsequent processing analogously includes the forming of an upper stack20 (FIGS. 1 and 1A) comprising second-alternating tiers 24, 26comprising different composition first and second-upper-stack materials44 and 30 elevationally over lower stack 22 and topping material 72.Upper stack 20 has an upper opening extending elevationally throughmultiple of second-alternating tiers 24, 26 in upper stack 20 and totopping material 72. Upper-stack-channel material 33 is formed in suchupper opening, with upper-stack-channel material 33 being ultimatelyelectrically coupled with lower-stack-channel material 33 inlower-stack-channel pillar 34. Alternate constructions to that shown byFIG. 1 may result in method implementations, and regardless of whether“gate first” or “gate last” processing is used. Regardless, control-gatematerial is provided laterally outward of the respective upper andlower-stack-channel materials. Further provided areinsulative-charge-passage material, charge-storage material, and acharge-blocking region of individual of the memory cells laterallybetween the control-gate material and the respective upper andlower-stack-channel materials.

Processing as described above may additionally occur or be modifiedslightly to produce, for example, the embodiment of FIGS. 8 and 8A.Specifically, and by way of example only, after filling remaining volumeof the lower opening with a laterally-central material that is laterallyinward of the dopant-diffusion barrier, both of laterally-centralmaterial 64 and lower-stack-channel material 33 may be elevationallyrecessed relative to elevationally-outermost surface 83 of insulatormaterial 54, 56. Such recessing of central material 64 andlower-stack-channel material 33 may occur while or during elevationallyrecessing dopant-diffusion barrier 62. Topping material 72 d could thenbe formed, and planarized back at least to elevationally-outermostsurface 83 of insulator material 54, 56 to produce an interveningconstruction 60 d like that shown in FIGS. 8 and 8A. In one embodimentand as shown, elevationally-outermost surface 66 of recesseddopant-diffusion barrier 62 is formed to be planar, as may be one orboth of elevationally-outermost surfaces of recessed central material 64and recessed lower-stack-channel material 33. In one such embodiment andas shown, elevationally-outermost surfaces of recessed dopant-diffusionbarrier 62, recessed laterally-central material 64, and recessedlower-stack-channel material 33 are formed to be co-planar. In one suchembodiment, topping material 72 d is formed directly against suchco-planar surfaces. Any other attribute(s) or aspect(s) as shown and/ordescribed herein with respect to other embodiments may be used.

Additionally, and by way of example only, a construction like oranalogous to that of FIGS. 9 and 9A may be constructed by forming theupper stack etc. immediately after forming the FIG. 17 construction.Upper channel material 33 may then be deposited into the recessesextending to surfaces 66.

Alternate example processing, for example to produce construction 10 gas shown in FIGS. 11 and 11A, is next-described with reference to FIGS.20-26. Like numerals from the above-described embodiments have been usedwhere appropriate, with some construction differences being indicatedwith the suffix “g” or with different numerals.

Referring to FIG. 20, such shows example alternate subsequent processingconducted on the substrate of FIG. 13 as compared to that of FIGS. 14and 15. Specifically, lower-stack-channel material 33 has been recessedwithin lower opening 80, and in one embodiment as shown to have anelevationally-outermost surface thereof that is planar and in one suchembodiment which is co-planar with that of insulator material 36.

Referring to FIG. 21, a material 85 has been formed to line andless-than-fill remaining volume of lower opening 80. Such may comprise adopant-diffusion-barrier material as described above where, for example,an elevationally innermost portion thereof will be used to formbase/bottom 70 as shown in FIGS. 11 and 11A.

Referring to FIG. 22, laterally-central material 64 has been formed inlower opening 80 as shown. Such material 64 comprises an uppermostregion 69 having conductivity-modifying dopant therein and a lowermostdopant-diffusion-barrier/base region 70. FIG. 23 shows exampleplanarizing of central material 64 back at least toelevationally-outermost surfaces of material 85.

Referring to FIG. 24, material 85 (not shown) has been subjected to asuitable anisotropic etch conducted selectively relative to the depictedexposed materials, leaving an annular space about central material 64 inone example.

Referring to FIG. 25, conductive-side material 74 is formed in loweropening 80 electrically coupled with lower-stack-channel material 33that is laterally-outward of central material 64. FIG. 26 shows removalof conductive-side material 74 and central material 64 back at least tothe elevationally outermost surface of insulator material 54, 56.

Subsequent processing as described above may then occur, for example anupper stack being formed that comprises second-alternating tierscomprising different composition first and second-upper-stack materialselevationally over the lower stack, the laterally-central material inthe lower opening, and the conductive material in the lower opening. Theupper stack is formed to have an upper opening extending elevationallythrough multiple of the second-alternating tiers and to at least one ofthe laterally-central material and the conductive material in the loweropening. Upper-stack-channel material is ultimately formed in the upperopening to be electrically coupled to the lower-stack-channel materialthrough conductive-side material 74 in the lower opening, for example toproduce a construction as shown in FIGS. 11 and 11A. Ultimately,control-gate material is provided laterally outward of the respectiveupper and lower-stack-channel materials. Also, ultimately provided areinsulative-charge-passage material, charge-storage material, and acharge-blocking region of individual of the memory cells laterallybetween the control-gate material and the respective upper andlower-stack-channel materials.

In one embodiment, the conductive material is formed to compriseconductively-doped-semiconductive material and in one embodiment isformed to comprise metal material. In one embodiment, theupper-stack-channel material is formed directly against thelaterally-central material, and in one embodiment is formed directlyagainst the conductive material. Any other attribute(s) or aspect(s) asshown and/or described herein with respect to other embodiments may beused.

An embodiment of the invention encompasses a method that is part of amethod of forming an elevationally-extending string of memory cells.Such comprises forming an intervening structure that is elevationallybetween upper and lower stacks that respectively comprise alternatingtiers comprising different composition materials. The interveningstructure is formed to comprise anelevationally-extending-dopant-diffusion barrier and laterally-centralmaterial that is laterally inward of the dopant-diffusion barrier andhas dopant therein. Some of the dopant from the laterally-centralmaterial is thermally diffused into upper-stack-channel material (e.g.,inherently occurring in subsequent processing and/or by exposing thesubstrate to 200° C. to 1,500° C. for 10 seconds to 10 hours in an inertatmosphere). The dopant-diffusion barrier is used during the thermallydiffusing to cause more thermal diffusion of said dopant into theupper-stack-channel material than diffusion of said dopant, if any, intolower-stack-channel material. Alternately stated or considered, thedopant-diffusion barrier functions as an asymmetric diffusion barrierthat is used during the thermally diffusing to cause more thermaldiffusion of said dopant into the upper-stack-channel material thandiffusion of said dopant, if any, into lower-stack-channel material.

In one embodiment, the intervening structure is formed to comprisedopant-transmissive-topping material above an elevationally-outermostsurface of the dopant-diffusion barrier. In such embodiment, thethermally diffusing comprises diffusing some of the dopant from thelaterally-central material through the dopant-transmissive-toppingmaterial and into the upper-stack-channel material. Any otherattribute(s) or aspect(s) as shown and/or described herein with respectto other embodiments may be used.

In this document, “elevationally-extending” and “extendingelevationally” refer to a direction that is angled away by at least 45°from a primary surface relative to which a substrate is processed duringfabrication and which may be considered to define a generally horizontaldirection. Further, “vertical” and “horizontal” as used herein aregenerally perpendicular directions relative one another independent oforientation of the substrate in three dimensional space. Further in thisdocument unless otherwise stated, “elevational(ly)”, “higher”, “upper”,“lower”, “top”, “atop”, “bottom”, “above, “below”, “under”, “beneath”,“up”, and “down” are generally with reference to the vertical direction.Also, “elevationally-extending” and “extending elevationally” withrespect to a field effect transistor is with reference to orientation ofthe transistor's channel length along which current flows in operationbetween the source/drain regions.

Further, “directly above” requires at least some lateral overlap (i.e.,horizontally) of two stated regions/materials/components relative oneanother. Further, use of “above” not preceded by “directly” onlyrequires that some portion of the stated region/material/component thatis above the other be elevationally outward of the other (i.e.,independent of whether there is any lateral overlap of the two statedregions/materials/components pillars)

Any of the materials, regions, and structures described herein may behomogenous or non-homogenous, and regardless may be continuous ordiscontinuous over any material which such overlie. Further, unlessotherwise stated, each material may be formed using any suitable oryet-to-be-developed technique, with atomic layer deposition, chemicalvapor deposition, physical vapor deposition, epitaxial growth, diffusiondoping, and ion implanting being examples.

Additionally, “thickness” by itself (no preceding directional adjective)is defined as the mean straight-line distance through a given materialor region perpendicularly from a closest surface of an immediatelyadjacent material of different composition or of an immediately adjacentregion. Additionally, the various materials or regions described hereinmay be of substantially constant thickness or of variable thicknesses.If of variable thickness, thickness refers to average thickness unlessotherwise indicated, and such material or region will have some minimumthickness and some maximum thickness due to the thickness beingvariable. As used herein, “different composition” only requires thoseportions of two stated materials or regions that may be directly againstone another to be chemically and/or physically different, for example ifsuch materials or regions are not homogenous. If the two statedmaterials or regions are not directly against one another, “differentcomposition” only requires that those portions of the two statedmaterials or regions that are closest to one another be chemicallyand/or physically different if such materials or regions are nothomogenous. In this document, a material, region, or structure is“directly against” another when there is at least some physical touchingcontact of the stated materials, regions, or structures relative oneanother. In contrast, “over”, “on”, “adjacent”, “along”, and “against”not preceded by “directly” encompass “directly against” as well asconstruction where intervening material(s), region(s), or structure(s)result(s) in no physical touching contact of the stated materials,regions, or structures relative one another.

Further, regions-materials-components are “electrically coupled”relative one another if in normal operation electric current is capableof continuously flowing from one to the other, and does so predominatelyby movement of subatomic positive and/or negative charges when such aresufficiently generated. Another electronic component may be between andelectrically coupled to the regions-materials-components. In contrast,when regions-materials-components are referred to as being “directlyelectrically coupled”, no intervening electronic component (e.g., nodiode, transistor, resistor, transducer, switch, fuse, etc.) is betweenthe directly electrically coupled regions-materials-components.

Additionally, “metal material” is any one or combination of an elementalmetal, a mixture or an alloy of two or more elemental metals, and anyconductive metal compound.

CONCLUSION

In some embodiments, a method that is part of a method of forming anelevationally-extending string of memory cells comprises forming anintervening structure that is elevationally between upper and lowerstacks that respectively comprise alternating tiers comprising differentcomposition materials. The intervening structure is formed to comprisean elevationally-extending-dopant-diffusion barrier andlaterally-central material that is laterally inward of thedopant-diffusion barrier and has dopant therein. Some of the dopant isthermally diffused from the laterally-central material intoupper-stack-channel material. The dopant-diffusion barrier during thethermally diffusing is used to cause more thermal diffusion of saiddopant into the upper-stack-channel material than diffusion of saiddopant, if any, into lower-stack-channel material.

In some embodiments, a method of forming an elevationally-extendingstring of memory cells comprises forming a lower stack comprisingfirst-alternating tiers comprising different composition first andsecond-lower-stack materials, insulator material above the lower stack,and a lower opening extending through the insulator material andmultiple of the first-alternating tiers. Lower-stack-channel material isformed in the lower opening. The lower-stack-channel material comprisesan elevationally-outermost portion that is against sidewalls of thelower opening and less-than-fills an elevationally-outermost portion ofthe lower opening. An elevationally-extending-dopant-diffusion barrieris formed around the lower opening laterally inward of theelevationally-outermost portion of the lower-stack-channel material.Remaining volume of the lower opening is filled with a laterally-centralmaterial that is laterally inward of the dopant-diffusion barrier. Afterthe filling, the dopant-diffusion barrier is elevationally recessedrelative to an elevationally-outermost surface of the insulator materialthat is adjacent the lower opening to form the dopant-diffusion barrierto have an elevationally-outermost surface that is lower than theelevationally-outermost surface of the insulator material that isadjacent the lower opening. Topping material is formed above theelevationally-outermost surface of the recessed dopant-diffusionbarrier. An upper stack comprising second-alternating tiers comprisingdifferent composition first and second-upper-stack materials is formedelevationally over the lower stack and the topping material. The upperstack has an upper opening extending elevationally through multiple ofthe second-alternating tiers and to the topping material.Upper-stack-channel material is formed in the upper opening and that iselectrically coupled with the lower-stack-channel material. Control-gatematerial is provided laterally outward of the respective upper andlower-stack-channel materials. Also provided areinsulative-charge-passage material, charge-storage material, and acharge-blocking region of individual of the memory cells laterallybetween the control-gate material and the respective upper andlower-stack-channel materials.

In some embodiments, a method of forming an elevationally-extendingstring of memory cells comprises forming a lower stack comprisingfirst-alternating tiers comprising different composition first andsecond-lower-stack materials, insulator material above the lower stack,and a lower opening extending through the insulator material andmultiple of the first-alternating tiers. Lower-stack-channel material isformed in the lower opening. Laterally-central material is formed in thelower opening and comprises an uppermost region having dopant thereinand a lowermost dopant-diffusion-barrier region. Conductive material isformed in the lower opening electrically coupled with thelower-stack-channel material that is laterally-outward of thelaterally-central material. An upper stack comprising second-alternatingtiers comprising different composition first and second-upper-stackmaterials is formed elevationally over the lower stack, thelaterally-central material in the lower opening, and the conductivematerial in the lower opening. The upper stack has an upper openingextending elevationally through multiple of the second-alternating tiersand to at least one of the laterally-central material and the conductivematerial in the lower opening. Upper-stack-channel material is formed inthe upper opening and that is electrically coupled with thelower-stack-channel material through the conductive material in thelower opening. Control-gate material is provided laterally outward ofthe respective upper and lower-stack-channel materials. Also providedare insulative-charge-passage material, charge-storage material, and acharge-blocking region of individual of the memory cells laterallybetween the control-gate material and the respective upper andlower-stack-channel materials.

In some embodiments, an elevationally-extending string of memory cellscomprises an upper stack elevationally over a lower stack, with theupper and lower stacks individually comprising vertically-alternatingtiers comprising control-gate material vertically alternating withinsulating material. An upper-stack-channel pillar extends throughmultiple of the vertically-alternating tiers in the upper stack and alower-stack-channel pillar extends through multiple of thevertically-alternating tiers in the lower stack.Insulative-charge-passage material, charge-storage material, and acharge-blocking region of individual of the memory cells is laterallybetween the respective upper and lower-stack-channel pillars and thecontrol-gate material. A conductive interconnect is elevationallybetween and electrically couples the upper and lower-stack-channelpillars together. The conductive interconnect comprises anelevationally-extending-dopant-diffusion barrier laterally outward of alaterally-central material. The dopant-diffusion barrier has anelevationally-outermost surface that is lower than anelevationally-outermost surface of the conductive interconnect.Conductive-topping material is above the elevationally-outermost surfaceof the dopant-diffusion barrier. An elevationally-extending-sidematerial is laterally outward of the dopant-diffusion barrier, with theside material being at least one of conductive and semiconductive.

In some embodiments, an elevationally-extending string of memory cellscomprises an upper stack elevationally over a lower stack, with theupper and lower stacks individually comprising vertically-alternatingtiers comprising control-gate material vertically alternating withinsulating material. An upper-stack-channel pillar extends throughmultiple of the vertically-alternating tiers in the upper stack and alower-stack-channel pillar extends through multiple of thevertically-alternating tiers in the lower stack.Insulative-charge-passage material, charge-storage material, and acharge-blocking region of individual of the memory cells are laterallybetween the respective upper and lower-stack-channel pillars and thecontrol-gate material. An intervening structure is elevationally betweenthe upper and lower stacks. The intervening structure comprises alaterally-central material having conductivity-modifying dopant thereinand an elevationally-extending-dopant-diffusion barrier laterallyoutward of the laterally-central material. The dopant-diffusion barrierhas an elevationally-outermost surface that is lower than anelevationally-outermost surface of the intervening structure. Toppingmaterial is above the elevationally-outermost surface of thedopant-diffusion barrier, with the topping material being dopanttransmissive. Conductively-doped-semiconductive material iselevationally between the upper-stack channel pillar and the lower-stackchannel pillar aside the topping material.

In some embodiments, an elevationally-extending string of memory cellscomprises an upper stack elevationally over a lower stack, with theupper and lower stacks individually comprising vertically-alternatingtiers comprising control-gate material vertically alternating withinsulating material. An upper-stack-channel pillar extends throughmultiple of the vertically-alternating tiers in the upper stack and alower-stack-channel pillar extends through multiple of thevertically-alternating tiers in the lower stack.Insulative-charge-passage material, charge-storage material, and acharge-blocking region of individual of the memory cells are laterallybetween the respective upper and lower-stack-channel pillars and thecontrol-gate material. A conductive interconnect is elevationallybetween and electrically couples the upper and lower-stack-channelpillars together. The conductive interconnect comprises conductive-sidematerial laterally outward of and extending elevationally along alaterally-central material. The lower-stack-channel pillar beingdirectly against the conductive-side material.

In compliance with the statute, the subject matter disclosed herein hasbeen described in language more or less specific as to structural andmethodical features. It is to be understood, however, that the claimsare not limited to the specific features shown and described, since themeans herein disclosed comprise example embodiments. The claims are thusto be afforded full scope as literally worded, and to be appropriatelyinterpreted in accordance with the doctrine of equivalents.

The invention claimed is:
 1. A method of forming anelevationally-extending string of memory cells, comprising: forming alower stack comprising first-alternating tiers comprising differentcomposition first- and second-lower-stack materials; forming aninsulator material above the lower stack; forming a lower openingextending through the insulator material and multiple tiers comprised bythe first-alternating tiers; forming a lower-stack-channel materialwithin the lower opening, the lower-stack-channel material being formedalong the first-alternating tiers and along the insulator material;forming an insulative material within a lower portion and an upperportion of the lower opening; recessing the insulative material withinthe lower opening to form an upper area of the lower opening that isunfilled; forming a dopant-diffusion barrier along sidewalls of theupper area within the lower opening laterally inward of thelower-stack-channel material; after forming the dopant-diffusionbarrier, filling a remaining volume of the upper area within the loweropening with a laterally-central material; after the filling, recessingan uppermost surface of the dopant-diffusion barrier relative to anelevationally-outermost surface of the insulator material to form arecessed surface of the dopant-diffusion barrier; forming a toppingmaterial above the recessed surface of the dopant-diffusion barrier;forming an upper stack comprising second-alternating tiers comprisingfirst- and second-upper-stack materials elevationally over the lowerstack and the topping material, the first-upper-stack material differingin composition relative to the second-upper-stack material, the upperstack having an upper opening extending elevationally through multipletiers comprised by the second-alternating tiers and to an elevationallevel of an upper surface of the topping material; forming anupper-stack-channel material within the upper opening and electricallycoupled with the lower-stack-channel material; providing a firstcontrol-gate material within the first-alternating tiers; providing asecond control-gate material within the second-alternating tiers;providing first insulative-charge-passage material, first charge-storagematerial, and a first charge-blocking region of individual memory cellscomprised by the elevationally-extending string of memory cellslaterally between the second control-gate material and theupper-stack-channel material; and providing secondinsulative-charge-passage material, second charge-storage material, anda second charge-blocking region of individual memory cells comprised bythe elevationally-extending string of memory cells laterally between thefirst control-gate materials and the lower-stack-channel material. 2.The method of claim 1 wherein the topping material is formed directlyagainst the recessed surface of the dopant-diffusion barrier.
 3. Themethod of claim 1 wherein the recessing of the dopant-diffusion barrierforms the recessed surface to be elevationally lower than anelevationally-outermost surface of the laterally-central material. 4.The method of claim 1 wherein the recessing of the dopant-diffusionbarrier forms the recessed surface to be elevationally lower than anelevationally-outermost surface of the lower-stack-channel material. 5.The method of claim 1 wherein the recessing of the dopant-diffusionbarrier forms the recessed surface to be elevationally lower than anelevationally-outermost surface of the laterally-central material andelevationally lower than an elevationally-outermost surface of thelower-stack-channel material.
 6. The method of claim 5 comprisingforming the upper-stack-channel material above the dopant-diffusionbarrier laterally between the dopant-diffusion barrier and thelower-stack-channel material.
 7. The method of claim 6 comprisingforming the upper-stack-channel material directly against theelevationally-outermost surface of the laterally-central material. 8.The method of claim 1 comprising, after the filling, elevationallyrecessing the laterally-central material and the lower-stack-channelmaterial relative to the elevationally-outermost surface of theinsulator material.
 9. The method of claim 8 comprising forming thetopping material directly against elevationally-outermost surfaces ofthe laterally-central material and the lower-stack-channel material anddirectly against the elevationally-outermost surface of the recessedsurface of the dopant-diffusion barrier.
 10. The method of claim 8wherein the elevationally recessing of the laterally-central materialand the lower-stack-channel material occurs during the elevationallyrecessing of the dopant-diffusion barrier.
 11. The method of claim 10wherein, the recessed surface of the recessed dopant-diffusion barrieris formed to be planar; the recessed laterally-central material isformed to comprise a planar-elevationally-outermost surface; therecessed lower-stack-channel material is formed to comprise aplanar-elevationally-outermost surface; and the recessed surface of thedopant-diffusion barrier, the recessed laterally-central material, andthe recessed lower-stack-channel material are formed to be co-planar.12. The method of claim 11 comprising forming the topping materialdirectly against the co-planar surfaces.
 13. The method of claim 1wherein the laterally-central material has conductivity-modifying dopanttherein, and further comprising: thermally diffusing some of theconductivity-modifying dopant from the laterally-central material intothe upper-stack-channel material, using the dopant-diffusion barrierduring the thermally diffusing to cause a greater amount of saidconductivity-modifying dopant to diffuse into the upper-stack-channelmaterial than into the lower-stack-channel material.